The present invention relates to the field of surveying movements of terrain, such as a landslide, a collapse, a vertical deformation of the terrain, or any other type of terrain movement.
It is necessary to survey terrain movements in particular in order to prevent damage to a building or to engineering work built on terrain where work is taking place.
Such a movement of terrain may also be due to work being carried out underground in the terrain.
For example, a terrain may have a tendency to collapse during construction of an underground work, such as a tunnel or foundation, for example.
Traditionally, terrain movements are surveyed by using one or more theodolites that sight survey targets arranged on the terrain or on the work that it is desired to survey.
More recently, attempts have been made to use satellite images for surveying the movements of survey points located on the terrain.
To do this, an interferometric study is carried out on the basis of a plurality of radar images of the terrain and a digital terrain model (DTM) of the terrain that is to be surveyed, it being specified that such data is easily available commercially.
During the study, a plurality of survey points situated in the terrain are selected. Nowadays there exist several algorithms for selecting survey points that have the feature of being clearly visible in radar images.
The survey points are thus selected so as to return to the satellite an echo of intensity that is sufficient to be seen on each pass of the satellite.
Point interferograms are then calculated.
The result of the interferometric study thus makes it possible, for the zone under study, to obtain a list of survey points, their raw coordinates, and also the raw variation in their coordinates.
However, it is known that those results are generally noisy and of variable quality. In other words, the raw coordinates and the raw variations of the coordinates as obtained by that method are found to be relatively inaccurate and therefore difficult to make use of in their current state.